Different modes and consequences of electron transfer in intercalation compounds Original Research Article

Intercalation reactions form one of the most versatile types of solid-state reactions known. Considering the layered host lattices they form an interesting access to artificial multilayers of very different properties. Many of these reactions are connected with redox processes. After a very short and general overview on the intercalation chemistry in layered host lattices, three different types of charge transfer accompanied with intercalation will be considered in detail and the consequence for the properties of the products will be discussed: (a) by means of electrointercalation into conducting host lattices (e.g. 2H-TaS2) electrons are transferred to the conduction band of the host accompanied with the simultaneous uptake of cations (here organic cations like methylene blue, methylviologen) in the interlayer space. Potential vs. time curves give valuable information about two-phase regions, homogeneity ranges and deviations from equilibrium. The consequence for the superconducting properties is shown; (b) treating the graphite intercalation compound C24(HSO4)(H2SO4) with strong oxidants leads to graphite oxide (GO). The oxidant is directly attached to the carbon network forming C–OH and C–O–C functions. Applying 13C MAS NMR of GO (and derivatives) we could identify the ether function as epoxide groups. This result has strong implications for the chemical behaviour of GO and could lead to new carbon networks; (c) clay minerals containing iron in the octahedral layers can undergo changes of the oxidation state of Fe-ions. We have found in vermiculites from Spain that Fe2+ can be oxidized completely to Fe3+, whereas the degree of reduction of the Fe3+ is rather restricted but varies with the composition of the clay. However, the extent of reduction can be strongly increased by heating the reduced samples.